Hi Val,
Be aware of the legal risks associated with list purchases. Basically, anyone on these lists would in fact receive unsolicited emails from you, which is not binding with the law in most of western countries, since the members of this list have not volunteered to be in relationship with your company.
The normal course would be that these brokers send emails from their systems on your behalf with a link to your landing pages. You would then only capture the consenting ones. These emails will have to clearly be sent from the broker and you should appear as a partner of them.
There are some real dangers in uploading a list into a Marketing Automation solution: the list may include spam traps and email to them could lead to severe damages to your email reputation and, as a consequence, to issues to other users of the Marketo email infrastructure.
If you really persist, you may want to use a third party email system and shoot this list from there, with CTA's to your Marketo LP's. Again, this will ensure that only consenting people will enter your Marketo database.
-Greg
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